Ceteris paribus, the mortality rate for potential deaths would have to be greater than 1/3 (33%) for both such that Choice B is preferable. However, given the smaller definite mortality rates, a 33% mortality rate for the remainder doesn't seem likely.

As it stands, in absolute numbers Choice A has a definite mortality rate of ~14%; Choice B has a definite mortality rate of ~21%. If that rate is carried over to estimate the potential mortality rate Choice A has total deaths ~27, Choice B as total deaths ~36.

More information would be nice, but given only the information provided; Choice A is preferable.